Drools 7.3.0 serialization null pointer exceptions with sliding windows

We have a fairly large rule-base with temporal reasoning and sliding windows.

While serializing the drools session we observe random null pointer exceptions as see below:

Exception in thread "pool-92-thread-98" java.lang.NullPointerException
at org.drools.core.rule.SlidingTimeWindow$BehaviorJobContextTimerOutputMarshaller.serialize(SlidingTimeWindow.java:323)
at org.drools.core.marshalling.impl.ProtobufOutputMarshaller.writeTimers(ProtobufOutputMarshaller.java:880)
at org.drools.core.marshalling.impl.ProtobufOutputMarshaller.serializeSession(ProtobufOutputMarshaller.java:210)
at org.drools.core.marshalling.impl.ProtobufOutputMarshaller.writeSession(ProtobufOutputMarshaller.java:118)
at org.drools.core.marshalling.impl.ProtobufMarshaller.marshall(ProtobufMarshaller.java:162)
at org.drools.core.marshalling.impl.ProtobufMarshaller.marshall(ProtobufMarshaller.java:146)
at com.mlnms.common.fmwk.drools.impl.DroolsClientImpl.backupKieSession(DroolsClientImpl.java:743)
at com.mlnms.common.fmwk.drools.impl.DroolsClientImpl.lambda$processStatefulEvents$0(DroolsClientImpl.java:506)
at java.lang.Thread.run(Thread.java:745)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)